The present invention is related to a microfiber nonwoven web. More specifically, the invention is related to a web containing superfine microfibers.
Microfiber webs, such as meltblown fiber webs, are well known, and meltblown fiber webs are described in various patents and publications, including Naval Research Laboratory Report 4364, "Manufacture of Super-Fine Organic Fibers" by V. A. Wendt et al.; Naval Research Laboratory Report 5265, "An improved Device for the Formation of Super-Fine Organic fibers" by K. D. Lawrence et al.; and U.S. Pat. No. 3,849,241 to Butin et al. Meltblown fiber webs, which contain thermoplastic microfibers generally having less than 10 .mu.m in average diameter, are produced by heating a polymer resin to form a melt, extruding the melt through die orifices in a die head to form filaments, directing a stream of heated fluid, usually air, toward the filaments exiting the die orifice to attenuated the filaments, and collecting the filaments on a foraminous surface to form a nonwoven web. Because the filaments are still tacky when they are collected, they form autogenous interfiber bonds to produce an integrated web.
Although conventional meltblown fiber webs contain fine microfibers, there is a need for fiber webs containing finer microfibers. There have been various attempts to reduce the diameter of meltblown fibers. One example of such attempts is reducing the polymer throughput to the die head. However, this direct controlling approach for producing fine meltblown fibers can only be used to reduce the fiber size to a limited extent since after a certain limit the reduction in through-put interrupts the fiber production altogether. Another exemplary process for producing fine meltblown fibers involves the steps of producing bicomponent conjugate meltblown fibers of an island-in-sea configuration and then dissolving the sea component of the meltblown fibers, thereby producing microfibers of the island component. However, the dissolving process is disadvantageous in that it requires a cumbersome dissolving step and it removes substantial portions of the conjugate fibers to produce fine fibers. Consequently, the dissolving process tends to be uneconomical and inefficiently utilizes the component polymers.
Yet another group of exemplary processes known in the art for producing fine fibers is split fiber production processes. However, known split fiber production processes may not be suitable for splitting meltblown fibers. The most widely used split fiber production process is a hydro-needling process, which utilizes a pressurized stream of water to split multicomponent conjugate fibers. In general, the process simultaneously splits and entangles the fibers to form a bonded nonwoven web. However, the hydro-needling process has not been used to produce split meltblown fiber webs since the autogenously bonded meltblown fiber webs, which have very fine breakable fibers and contain substantially uniformly distributed numerous interfiber bonds that restrict fiber movements, are difficult to split with the mechanical splitting process.
There are other fine microfiber webs known in the art, and they include glass microfiber webs. Although superfine glass microfibers can be produced, the glass microfibers are brittle and, thus, are not suitable for applications in which strength properties of the fibers are important.
There remains a need for superfine microfiber webs and a production process for producing the webs.